As described in class, what does the sender send to the receiver when using hashing for integrity and authentication? (Do not include information previously shared / agreed upon by the sender and receiver.)

The answer is "secret key k".

Explanation:

When the sender sends the message, he/she may combine, it with the hidden key, and determines the hashing, when transmitting the information the digest is being sent, and also the message is transmitted through the connection.

when the receiver receives the message, still having the very same secret key, adding the Hidden Key then recalculating the hashing again. In this, two factors if another subsequent digest matches something, this message is sent.  

the only way i would see could be an autoclicker type software. but that is very time consuming.